A technology for improving fuel economy and exhaust performance by automatically stopping (idle stop) an engine while a vehicle is stopped has been put to practical use.
Since a mechanical oil pump cannot be driven by power of the engine while the engine is automatically stopped in a vehicle adopting this technology, a hydraulic pressure necessary at startup cannot be supplied from the mechanical oil pump to a starting frictional engagement element of the automatic transmission (brake, clutch to be engaged at startup) and the starting frictional engagement element is set in a non-engaged state. In this case, even if it is tried to start the vehicle in response to a start request, the engagement of the starting frictional engagement element is delayed, wherefore the vehicle cannot be quickly started.
Thus, in JP2002-106380A, an electrical oil pump which is driven by electric power supplied from a battery is separately provided to supply a hydraulic pressure produced by the electrical oil pump to the starting frictional engagement element while the engine is automatically stopped.